1888.] G. M. Gihs— Notes on the Ampliipoda of Indian Waters. 229 



the depth of the head and more than a third of its breadth. In length, it 

 considerably exceeds half the length of the head, the oesophagus opening 

 into it rather in front of the middle of its length. It is lined thronq;h- 

 OTit with chitine, and presents sundry toothed plates and hairs which 

 subserve the trituration of food. Of these plates and hairs, the follow- 

 ing are the most remarkable : from the anterior wall of the cavity, 

 on either side of the middle line, projects a strong flattened plate 

 somewhat narrowed at its origin from the wall of the cavity and 

 expanded at its border, which latter is arm(;d with a double row of 

 strong teeth, very like those on the triturating plate of the man- 

 dible ; the upper ranks of these teeth are short, strong, and some- 

 what lanceolate in form, while the lower ranks are longer, thinner, 

 and of more uniform thickness, and interdigitate with a series of 

 similar long weak teeth placed on a second pair of plates situated on the 

 anterior portion of the ventral wall of the organ (Plate II, fig. 3.). 

 Lastly, the middle part of the dorsal wall of the organ is densely 

 clothed with long thin flexible hairs. From the vicinity of the posterior 

 end of the ventral wall, rather nearer the posterior end of the organ 

 than to the point of entry of the oesophagus, a funnel-shaped depression 

 leads to a very short channel, which admits the food to a second chitin- 

 lined cavity, which I have already alluded to as the " sifting stomach." 

 Seen in transverse section this latter cavity has a cordate outline ; a 

 strong chitinous ridge, with a very broad base, projecting upwards into 

 its lumen from its ventral wall, and reaching upwards nearly to the 

 level of the dorsal wall of the organ, thus dividing the greater part of 

 the length of the cavity into two nearly distinct spaces. In front and 

 behind, this ridge sinks down rapidly to the level of the ventral wall of 

 the cavity. Each of the two main spaces into which the viscus is thus 

 cut off is further subdivided by a very delicate chitinous plate which 

 projects upwards and inwards nearly as high as the main median ridge. 

 These plates, the median ridge, and the walls of the viscus are alike 

 clothed with closely set, short, and stiff, but very fine, hairs, so that the 

 entire organ must form a most efficient sieve by which all particles that 

 have not been sufficiently comminuted in the gizzard are kept from 

 entering the mid-gut. The " sifting stomach " opens behind by a 

 constricted channel into the mid-gut. The mid-gut is of considerable 

 dimensions, and is perfectly straight and of nearly uniform diameter 

 throughout, it opens by a narrow anus on the under surface of the 

 sixth abdominal segment close to the telson. In its anterior portion the 

 endothelial coat is two cells in thickness and the mesoblastic layer 

 of perceptible thickness. In the hinder part of the canal, however, 

 the endothelium is reduced to a single row of cells and the meso- 



